Hearing assistance devices come in a variety of devices including but not limited to assistive listening devices, cochlear implants and hearing aids. Hearing assistance devices are useful in improving the hearing and speech comprehension of people who have hearing loss by selectively amplifying certain frequencies according to the hearing loss of the subject. A hearing aid typically has three basic parts; a microphone, amplifier and a speaker. The microphone receives sound (acoustic signal) and converts it to an electrical signal and sends it to an amplifier. The amplifier increases the power of the signal, in proportion to the hearing loss, and then sends it to the ear through the speaker. Cochlear devices may employ electrodes to transmit sound to the patient.
When the hearing loss is severe and a significant amplification is needed from the hearing aid's amplifier, acoustic feedback becomes an issue. Acoustic feed back occurs when there is a feed back loop from the microphone to the receiver (speaker) of the hearing aid which leads to a howling sound produced by the hearing assistance device. This feedback is both annoying and reduces the maximum usable gain of the hearing aid.
Acoustic feedback is a primary obstacle to a normal use of a telephone with hearing aids. The presence of a handset with in few millimeters of the hearing aid's microphone reflects amplified sound leaking from the ear canal back through the hearing aid. As the hand set approaches the hearing aid, the frequency and intensity of the reflected signal increases to the point where the hearing aid becomes unstable and components begin to ring.
To solve this feedback problem with telephone use, modern hearing aids have an additional component, a telecoil, to pick up the signal from the headset magnetically. When a hearing aid has a telecoil, it has two modes of operation; acoustic and magnetic. Switching between these two modes can be done manually, by pressing a mode switch, or in some hearing aids it is done automatically, by incorporating a magnetically-activated switch. In the later case, the sensor senses the magnetic field of the handset's biasing magnet and switches the mode to telecoil-mode.
While this solution solves the problem with land-line phones which are compatible with hearing assistance devices, the magnetic field generated by the cell phone's speaker is not strong enough to trigger the magnetic-activated switch in the hearing assistance devices. Thus, there is a need in the art for an improved method and apparatus for detecting cellular telephones using hearing assistance devices.